Lysolecithin, Newcastle disease virus, and Sendai virus were used separately for inducing the fusion and nuclear transfer between mouse egg cells. Two-cell eggs with one blastomere damaged are better than pronuclear eggs for initiating the cell fusion-nuclear transfer experiments because of their higher viability against the manipulation treatments. Advanced embryogenesis was, however, prevented by multinucleation, or polykaryocytosis. Therefore, experiments for inactivation of the nucleus of mouse eggs are being performed by using ultraviolet irradiation to prevent the development of polyploidy before an egg cell is fused with another cell to receive a nucleus. The technique of egg mircomanipulation was employed to pipette virus-cell suspension into the perivitelline space to achieve the cell fusion- nuclear transfer within the zona pellucida. The possibility of re- aggregation and development of dissociated blastomeres has been tested in the droplet cultures. Whether or not a procedure of culturing or micromanipulation of egg cells will affect the development of sensitivity to teratogenesis is also being investigated.